1. Field of the Invention
This invention generally relates to a tide gate valve and, more particularly, to such valves for use on large-sized storm sewer pipes having diameters on the order of 24 inches.
2. Description of the Prior Art
A check valve is essentially a valve which allows fluid flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the initial fluid pressure head. One variety of check valve which has been developed in recent years entails a flexible, resilient sleeve which terminates with a symmetrically tapered duck-bill configuration and a rectilinear outlet end which opens to an oval or circular shape to accommodate successively greater fluid flow, but which closes on back pressure build-up. One problem with such valves, especially in larger sizes, is that when a high back pressure is induced, the duck-bill sleeve collapses and inverts, thus permitting back flow of fluid.
The fluid back-flow problem is especially acute when such valves are used to handle storm sewer effluent. Virtually all municipalities near waterways have storm sewer pipes which empty into the waterways. When there is a storm, storm water from the streets runs into these sewer pipes and flow into the waterways. When the tide is in, these sewer pipes back fill with the water from the waterway. This leaves no or reduced storage capacity in the sewer pipes. In the event there is a large cloudburst or storm during the time that the tide is in, all or a portion of the storm water cannot get into the sewer because the sewer pipes are at least partially filled. This causes street flooding.
To deal with the street flooding problem, various types of tide gate valves have been proposed. One type consists of a wooden gate which floats up when the tide comes in, thereby closing the tide gate valve to prevent the sewer pipes from filling with the tide water. When the tide goes out, the wooden gate sinks, thereby opening the tide gate valve. Another type consists of a mechanical tide gate valve made of steel which, however, is subject to corrosion from salt water. Such previously proposed tide gate valves are also subject to jamming when trees, logs, bricks and the like get into the valves and prevent the gates from fully closing.
For large-sized sewer pipes on the order of 24 inches or even greater diameter, one design problem is inversion, because the larger the diameter of the valve, the larger the area of the valve and, in such cases, even a low back pressure multiplied times a large valve area will invert and collapse the flexible sleeve of the valve, thus allowing reverse flow of fluid to take place. A related design problem concerns the ease of opening the valve. The more one attempts to design the valve to resist inversion, the less easy the valve is to open. Thus, if one constructs the valve with rigid materials, the valve will certainly resist inversion and sagging, but at the expense of opening the valve. The reverse situation also is true. That is, if one constructs the valve with very flexible materials, the valve will certainly open easily, but at the expense of resisting inversion and of causing the valve to sag.
An improved tide gate check valve suitable for large-sized conduits such as storm sewer pipes was disclosed in U.S. Pat. No. 4,492,253 and in our allowed U.S. patent application Ser. No. 754,819, filed July 12, 1985, entitled INVERSION-RESISTANT TIDE GATE VALVE, and assigned to the same assignee as the instant application.